Recent Research Trends in Genetic Algorithm Based Flexible Job Shop Scheduling Problems

Table 1

Commonly used FJSSP objective functions.

Measure	Symbol	Formula	Meaning	Impact/applicability
Makespan			The time taken to complete all jobs	Minimizing makespan will directly minimize the production cost
Mean completion time			Average time required for completion of a single job	Minimizing this will directly reduce the production cost
Maximum Flowtime			The time that a job j spends in a shop while the processing takes place or while waiting	The longer the time a job spends on the production floor, the bigger its cost
Total tardiness			The positive difference between the completion time and due date of all jobs	Applicable when early jobs do not give a reward but late jobs are penalized
Average tardiness			Average difference between the completion time and due date of a single job	Applicable when overall production is required to be completed in a stipulated time
Total weighted tardiness			Sum of weighted difference between the completion time and due date of a job	Applicable when some jobs are more important than others
Maximum lateness			The maximum slack of a job with respect to its due date	Applicable when early jobs give a reward
Number of tardy jobs			Number of jobs that are late	Directly affects the production cost and machine availability
Total workload of machines			The total working time on all machines	Ensures maximum utilization of machines